METAMORPHIC STUDIES 357 
forces of the chemical reactions with the surface elements or 
expansive forces mechanically locked up in crystalline structure 
are but feebly resisted by gravity. The rock adapts itself to the 
new conditions of equilibrium. Unconsolidated sediments, when 
buried beneath the surface, reach new conditions of temperature 
and pressure, and readjustment is required to establish a condition 
of energy equilibrium. The constituents of the sediments are 
forced together by gravity, and energy is locked up in the mole- 
cular combinations, only to be lost again as the rock later comes 
under katamorphic conditions. 
If heat is permanently lost by the pulsational or cyclic changes, 
while gravity remains constant, it may be supposed that the energy 
available for rock change at a given depth becomes lower. In order 
that the rock may fully complete its cycle by storing up energy in 
one phase equal to that lost in another it must go to a point deeper 
within the earth, where increased effect of pressure can make up 
for the loss of heat during the cycle. The running down of energy 
therefore implies the permanent accumulation of metamorphic 
products instead of reproducing igneous rocks on the original scale. 
The probable incompleteness of the metamorphic cycle, as 
inferred from energy changes, is more satisfactorily indicated by 
field evidence to be noted below. 
GEOLOGICAL EVIDENCE THAT CYCLE IS NOT CLOSED 
1. Subcrustal fusion.—Completion of the cycle would involve 
reproduction of igneous rocks from sediments wherever they have 
reached sufficient depth—so-called subcrustal fusion. So far as 
observation goes, the common results of anamorphism are schists 
and gneisses characterized by greater abundance of platy and 
columnar minerals than the original igneous rocks. Locally, near 
igneous contacts, anamorphism reproduces rocks indistinguishable 
from the original igneous rocks. We do not attempt to show that 
subcrustal fusion has not occurred on some scale, but believe that 
there is no adequate evidence within our zone of observation that 
this has been accomplished on a large enough scale to complete the 
metamorphic cycle for anything but a small proportion of meta- 
morphosed rocks. The lowest known rocks of the geological 
